Immediate solutions: Lean burn at best economy for gasoline engines. Deleting EGR ... 16.2 (lean burn for Best. Economy*
Highly‐fuel‐efficient Automobiles via Promoted NOx Decomposition (PND) by Electro‐Catalytic Honeycomb (ECH)
Ta-Jen Huang, Professor (
[email protected])
Department of Chemical Engineering National Tsing Hua University Hsinchu, TAIWAN 1
How to achieve high fuel‐efficiency of automobiles Issues • Highest possible combustion temperature ↔ highest possible fuel efficiency [thermal efficiency]
→ Complete combustion of all precursors of combustible pollutants → Gasoline direct‐injection compression ignition (GDCI) engine fueled with light gasoline [light un‐branched open‐chain hydrocarbons (HCs)] ← no PM (particulate matter) *** Immediate solutions: Lean burn at best economy for gasoline engines Deleting EGR (exhaust gas recirculation) of diesel engines for highly‐increased fuel efficiency → Zero pollution of CO, HCs & PM. The remaining issue is high NOx control.
• Removal of high to low concentration NOx under oxygen‐rich condition → Removing very high NOx to near‐zero & completely oxidizing CO & HCs. • NOx emission control at engine cold‐start → No delay on NOx control. • No consumption of reducing agent on NOx control → No remain of the reducing agent, e.g. NH3, to cause secondary pollution. All these issues solved by Electro‐Catalytic Honeycomb (ECH).
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The real‐world applicability of PND by ECH is confirmed by experimental data shown in the following.
How to increase the fuel efficiency of current gasoline automobiles? For gasoline cars, simply change the Air Fuel Ratio from 14.7 (stoichiometric burn) to 16.2 (lean burn for Best Economy*) [*as shown on the right].
This only needs to replace the Three‐way Catalytic (TWC) converter with the ECH. 3
How to increase the fuel efficiency of current diesel automobiles? For diesel cars, deleting EGR to highly increase the fuel efficiency and also to highly simplify the aftertreatment system (to one ECH only). This only needs to replace the Diesel oxidation catalyst (DOC) converter to the ECH and For new cars: deleting all other units (including all sensors) in the aftertreatment system. For old cars: simply close EGR and stop operating all other units (including all sensors’ electrical heating) in the aftertreatment system. 4
Gasoline direct‐injection compression ignition (GDCI) engine for very high fuel efficiency with zero pollution
EGR is not needed via ECH-deNOx GDCI can be for 2 & 4 cycle engine
• GDCI engine fueled with light gasoline [light un‐branched open‐ chain hydrocarbons ↔cetane] can have a fuel efficiency higher than current gasoline engine by 50% [a reduction of greenhouse gas emission by 50%] with zero pollution of CO & HCs without PM.
[S. Chu, A. Majumdar, Nature 488 (2012) 294; M.A. Ghadikolaei, Int. J.
Res. Eng. Tech. 3 (2014) 335]
• Light un‐branched open‐chain HCs [cetane]: alkane molecules with a cetane number of 100 ‐‐ can ignite very easily under compression.
• Fuels with higher cetane number have shorter ignition delays →more complete combustion↔less HCs & CO emission→zero pollution →higher combustion temperature↔higher expansion power →higher NO ←welcome by PND →less engine knocking↔more smooth and quiet engine 5 x
Current 2 cycle gasoline engine → GDCI can increase the fuel efficiency by 60% & be pollution free [intake fuel vapor → intake air]
Electro‐Catalytic Honeycomb (ECH)‐deNOx —
a real‐world device for Promoted NOx Decomposition (PND) • Lower emission of greenhouse gases (GHG) needs higher fuel efficiency, i.e., lower fuel (energy) consumption → cost down via PND.
• Currently, fuel efficiency is inhibited by difficulty in deNOx technologies (SCR reductant supply, NSR storage capacity limit…) to treat an exhaust with high NOx concentration. •
TWC can not treat lean‐burn exhaust.
• Higher combustion temperature leads to higher fuel efficiency but also higher NOx concentration in the exhaust. This is inevitable since the following reactions occur during combustion using air (N2 + O2 ): Initiation: O2 → 2O (thermal cracking — providing O for combustion) Chain reaction: O + N2 → NO + N; N + O2 → NO + O Termination: NO + O → NO2
• This deNOx difficulty has been resolved by PND with ECH promoted NO decomposition for automotive emission control. 6
x
Electro-catalytic honeycomb (ECH) enables saving health & fuel Diesel exhaust causes cancer (WHO 2012.6.12) World Health Organization -- Diesel engine exhaust fumes are a definite cause of lung cancer. soot
NOx
outdoor air pollution also (WHO 2013.10.17)
→ What should we do? Not driving diesel automobiles? → Deleting EGR needing diesel particulate filter **
NOX‐soot trade‐off during EGR of diesel engine
Old tech e.g. SCR (Selective Catalytic Reduction)
Current diesel engines have sacrificed the fuel efficiency to lower NOx concentration by exhaust gas recirculation (EGR)
[A. Maiboom et al., Energy 33 (2008) 22]
Deleting EGR
soot: particulate matter (PM)
Deleting EGR ↓
** Note: The very small particulates, which can go through the filter, can penetrate deep into the lung. [American Lung Association/Calif.]
→ Deleting EGR : saving both health & fuel
→Increase combustion temperature in engine → Increased NOx (%)
New tech (PND) preferred → Increasing fuel efficiency at least by burning more soot precursor in the engine → reduce soot emission 7
The most efficient lean‐burn combustion processes are that of gasoline engine being converted from stoichiometric-burn to lean-burn & that of diesel engine deleting EGR for best economy
>30% auto’s fuel saving ← deNOx by Electro-Catalytic Honeycomb (ECH)
ECH looked the same as TWC (Three‐way Catalytic) converter -- for stoichiometric-burn engine
ECH-deNOx reactor
for lean-burn engine
Engine exhaust pipe
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Electro-Catalytic Honeycomb (ECH) for
promoted NOx decomposition
lean NOx emission control
The ECH works on Promoted NOx Decomposition (PND), i.e. emf-promoted direct NOx decomposition,
electrochemical cell (generating emf)
NOx (NO+NO2) → N2+O2
electrochemical cell (generating emf)
Typical deNOx characteristics of PND are*: •
promoted NOx decomposition
Electromotive force (emf) is generated when there is a difference in oxidation/reduction potentials of Cathode/Anode and increases with potential difference.
The EDC consists of two electrochemical cells. [electrochemical double-cell]
ECH
[EU patent EP 2724768 & other patent applications]
•
• • •
10: Electro-catalytic honeycomb (ECH) 11: Anode, forming ECH structure 111 & 112: outer & inner surface of the anode structure 12: Exhaust flow channel 13: Shell, covering the outer surface of the anode structure 20: Electrolyte layer, coated on the inner surface of the anode structure 30: Cathode layer, facing the exhaust flow channel for exhaust treatment
[as automotive catalytic converter]
•
No consumption of reducing agent or else [purely decomposition] Care free Higher O2 concentration results in higher deNOx rate [due to increased promotion with emf] Simultaneous oxidation of hydrocarbons, CO & Particulate Matter (PM) feasible Higher NO concentration can result in higher deNOx rate [obeying reaction kinetics] Highly fuel‐efficient engines Relatively constant deNOx rate at very low NOx concentration [due to a specific reaction mechanism] near‐zero NOx emission can be achieved No temperature window & effective deNOx from ambient temperature no treatment delay & deNOx at cold weather Presence of H2O & CO2 beneficial & SO2 OK; no N2O formation No use of precious metal Economical
• *These characteristics are all based on the inventor’s published results.
Typical experimental results on promoted
NOx decomposition (PND)
diesel exhaust
diesel exhaust
diesel exhaust
-1 -2 deNOx rate (mole NOx‧min ‧cm )
[T.J. Huang et al., Appl. Catal. A 445–446 (2012) 153]
7
1800 ppm NOx 360 ppm NOx
0.3
6 0.2 5
4 100
150
0.1 200
-1 -2 deNOx rate (mole NOx‧min ‧cm )
[T.J. Huang et al., Appl. Catal. B 110 (2011) 164]
○ Temperature ( C)
no treatment delay & no temperature window
Very high NO concentration preferred [T.J. Huang et al., Chem. Eng. J. 203 (2012) 193]
Relatively-constant deNOX rate at low NOX region
These are typical characteristic curves for promoted NOx Decomposition for lean deNOx of combustion processes
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deNOx characteristics of
emf‐promoted decomposition of NOx • Very high NO concentration preferred Highly fuel‐efficient engines & ECH‐deNOx does not need any control on diesel engine operation
• No consumption of reductant or anything else Care free • Effective at high O2 concentration the higher the better Simultaneous oxidation of hydrocarbons, CO & PM feasible
• No temperature window & effective deNOx from ambient temp no treatment delay & deNOx at cold weather
• Relatively constant deNOx rate at very low NOx concentration near‐zero NOx emission can be achieved Very compact size for automobiles • ECH similar size to SCR converter • No use of precious metal Economical • H2O & CO2 beneficial & SO2 OK; no N2O formation • Zero pollution (shown next)
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Real‐world automotive applications For SCR‐deNOx onboard of heavy‐duty Diesel vehicles with commercial
ECH-deNOx on
real engine exhaust
V2O5/WO3–TiO2 catalyst on standard metal substrates with a cell density (~honeycomb) of 400 cpsi, the highest
activity for 1000 ppm NO at 52,000 h−1 & 400 °C is The ECH-deNOx activity 1.24 μmole NO∙min‐1∙cm‐2 is comparable to the ECH-deNOx double this as shown on the right
[O. Krocher, M. Elsener, Appl. Catal. B: Environ. 75 (2008) 215]
ECH-deNO comparable Note: SCR‐deNOx activity of as shown on the right 0.024 μmole NO∙min‐1∙cm‐2 was reported for treating 250 ppm NO with catalyst plate. x
[X. Fan et al., Catal. Commun. 12 (2011) 1298]
real-world automotive SCR-deNOx activity. 12
Shortages in current automotive deNOx technologies
• Three‐way catalytic (TWC) converter (honeycomb) Engine operation must be adjusted to accommodate the exhaust treatment. The usage of precious metals. Stoichiometric burn — low fuel efficiency. Treatment delay ‐‐ the catalyst is not effective at ambient temperature and thus a heating period is required. [for all current deNOx via reduction or storage]
• Exhaust Gas Recirculation (EGR)
To result in low NOx concentration in exhaust at the expense of fuel efficiency.
• Selective Catalytic Reduction (SCR)
The consumption of reducing agents, e.g., ammonia in urea‐based SCR (costly & inconvenient refilling). The formation of N2O from NO, a strong greenhouse gas. with presence of reducing agent
• NOx Storage and Reduction (NSR) — lean‐NOx trap The consumption of fuel for NOx treatment. Limited storage capacity.
• Electrochemical NOx Reduction with applied voltage (electrical current) The consumption of electricity with low current efficiency.
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Principle for emf-promoted decomposition NOx: NO & NO2 NO N + O (previously needing removal by reductant NH ,CO,HCs) SCR↑,TWC↑ ↓ ↓ N2 O2 (continuously promoted oxygen desorption‐‐PND) ↑ NO2 NO + O O2 2O SOx: SO2 & SO3 SO2 → 1/8S8 + 2O → O2 (promoted oxygen desorption) SO3 SO2 + O 3
promoted NOx decomposition--PND promoted SOx decomposition--PSD
continuously promoted
oxygen desorption by the presence of a voltage
(an electromotive force, emf)
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Publications supporting
lean deNOx by promoted NOx decomposition (PND) underlined is the inventor of the ECH.
• • • • • • • • • • • • • • • • • • •
Power generation Ta‐Jen Huang, C.L. Chou, Electrochem. Comm., 11 (2009) 477–480. with NOx substituting O2 Ta‐Jen Huang, C.L. Chou, J. Power Sources, 193 (2009) 580–584. -- NOx decomposition in rich oxygen Ta‐Jen Huang, C.L. Chou, J. Electrochemical Society, 157 (2010) P28–P34. -- promoted by both voltage Ta‐Jen Huang, C.L. Chou, Chem. Eng. J., 160 (2010) 79–84. & oxygen-ion migration Ta‐Jen Huang, C.L. Chou, Chem. Eng. J., 162 (2010) 515–520. Ta‐Jen Huang, I.C. Hsiao, Chem. Eng. J., 165 (2010) 234–239. Ta‐Jen Huang, C.Y. Wu, Y.H. Lin, Environmental Science Technology, 45 (2011) 5683–5688. Ta‐Jen Huang, C.Y. Wu and C.C. Wu, Chem. Eng. J., 168 (2011) 672–677. NOx decomposition at (promoted by) Ta‐Jen Huang, C.Y. Wu, C.C. Wu, Electrochem. Comm., 13 (2011) 755–758. open-circuit voltage (electromotive force, emf) Ta‐Jen Huang, C.Y. Wu, C.C. Wu, Chem. Eng. J., 172 (2011) 665–670. Ta‐Jen Huang, C.Y. Wu, S.H. Hsu, C.C. Wu, Energy Environmental Science, 4 (2011) 4061–4067. Ta‐Jen Huang, C.H. Wang, Chem. Eng. J., 173 (2011) 530–535. Ta‐Jen Huang, C.Y. Wu, S.H. Hsu, C.C. Wu, Appl. Catal. B: Environmental, 110 (2011) 164–170. Ta‐Jen Huang, C.Y. Wu, Chem. Eng. J., 178 (2011) 225–231. Ta‐Jen Huang, C.H. Wang, J. Electrochemical Society, 158 (2011) B1515–B1522. Ta‐Jen Huang, S.H. Hsu, C.Y. Wu, Environmental Science Technology, 46 (2012) 2324–2329. Ta‐Jen Huang, C.Y. Wu, D.Y. Chiang, C.C. Yu, Chem. Eng. J., 203 (2012) 193–200. Ta‐Jen Huang, C.Y. Wu, D.Y. Chiang, C.C. Yu, Appl. Catal. A: Gen., 445–446 (2012) 153–158. 15 Ta‐Jen Huang, C.Y. Wu, D.Y. Chiang, J. Ind. Eng. Chem., 19 (2013) 1024–1030.
emf ↔open‐circuit voltage (OCV) of fuel cell
no anode fuel needed
with applied voltage — oxygen pumping
Anode fuel: HCs etc.
with power generation — solid oxide fuel cell (SOFC) ‐‐ continuous presence of an OCV for power generation
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O2 + 2e− 2O− Oxygen can be simply desorbed 2O− → O2 without discriminating the source of O
NOx ↕ O
Schematic description of bi‐pathway dominated oxygen reduction on SOFC cathode [M. Gong, R.S. Gemmen, X. Liu, J. Power Sources 201 (2012) 204]
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Lean deNOx by emf-promoted decomposition of NOx NO → N + O NO2 → N + O2
at high enough NO concentration
∆H298 = -21.6 Kcal/mole (exothermic) ∆H298 = -8 Kcal/mole
2NO + [ ]·[ ] → N－[O]·[O]－N N－[O]·[O]－N → N2 + [O]·[O] [O]·[O] → O2 + [ ]·[ ]
2nd order rN2 = k [NO]2
Higher NO concentration is highly preferred (according to kinetic law)
2NO → N2 + O2
The presence of a voltage weakens the chemisorptive bond strength of the O species. [C.G. Vayenas, S. Bebelis, Catal. Today 51 (1999) 581]
facile desorption of oxygen for emf-promoted decomposition of NOx 18
-1 -1
N2 formation rate ( mol min g )
emf-promoted decomposition of NO → N2 + O2 5000 4500 4000 3500 3000 25
1500
12
1000
8
500
4
Room temperature
0 0
The deNOx rate via emf-promoted decomposition is two orders higher than that over conventional catalyst via direct decomposition
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ECH Catalyst
500
1000
1500
2000
0
2500
Inlet NOx concentration (ppm)
ECH can have a relatively-constant deNOx rate while Catalyst honeycomb cannot.
20 15
solid oxide fuel cell
10
cell at OCV catalyst powder
5 0 1000
2000
3000
4000
5000
6000
OCV: open-circuit voltage
(solid oxide fuel cell operation without consuming anode fuel, i.e., reductant) ~ electromotive force (emf )
Inlet NO concentration ( ppm ) solid oxide fuel cell：LSC –GDC cathode catalyst：LSC –GDC (La0.6Sr0.4CoO3 –Ce0.9Gd0.1O1.95)
14% O2, 10% H2O, 10% CO2; 600oC
-1 -1 deNOx rate (mole NOx‧min ‧g )
Principle and proof for
-1 -1 deNOx rate (mole NOx‧min ‧g )
ECH vs. Catalyst honeycomb 2000
Over the catalyst in a conventional reactor, the formed N species from direct NO decomposition can be easily associated to form N2; however, the formed O species is strongly adsorbed and facile desorption of the O species as O2 into the gas phase is very important. [Y. Teraoka et al., J. Chem. Soc. Faraday Trans. 94 (1998) 1887]
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The fields for applications of ECH The application fields of ECH
Schematics of ECH
Light‐Duty Vehicles and Trucks
Heavy‐Duty Highway Engines and Vehicles Compression‐ignition (CI) engines [GDCI]
Urban buses Trucks (ECH‐deNOx) Long distance buses Recreational vehicles Long haul trucks Spark-ignition (SI) engines → Lean burn
Nonroad Engines and Vehicles Aircraft CI engines (underground mining, sea oil platform…) Locomotives (ECH‐deSOx & deNOx) Marine CI engines Recreational engines and vehicles Stationary sources
Electro‐catalytic honeycomb (ECH)
Gasoline passenger cars & Motorcycles Diesel passenger cars (ECH‐deNOx) Pickup trucks
Power plant boilers (burner), Gas turbines Fertilizer plants, Cement plants Large boilers (ECH‐deSOx & deNOx) Medium boilers (in Hospitals, Care centers…) Small boilers (Household boilers) Other Combustion exhausts (ECH‐deSOx & deNOx)
EDC
10: ECH; 11: anode, forming the structure of the ECH; 111 and 112: outer and inner surface of the anode structure, respectively; 12: exhaust flow channel; 13: shell, covering the outer surface 111; 20: electrolyte layer, coated on the inner surface 112; 30: cathode layer, facing the exhaust flow channel for exhaust treatment. (EU patent EP 2724768) SO2→ 1/8S8+O2
Seal*
Metal plate
EDC plate for PND testing with or without metal plate
Electrochemical double‐cell (EDC) * The anode side should be enclosed completely by dense layer (seal).
Concluding Remarks • Lean deNOx by promoted NOx decomposition (PND) no consumption of reductant (no NH3 slip) or other resource • Higher O2 concentration preferred for deNOx simultaneous oxidation of hydrocarbons (HCs), CO & Particulate Matter (PM) feasible • Very high NO concentration preferred for deNOx ↔ very high temperature in engine allow deleting EGR minimize HCs, CO & PM formation in engine • Relatively constant deNOx rate at very low NOx concentration
near‐zero NOx emission can be achieved • No temperature window & effective deNOx from ambient temperature no treatment delay Thus, especially with GDCI (light Gasoline Direct‐injection Compression Ignition) engines, ECH‐deNOx can result in
zero pollution of automobiles to help Creating Healthy, Livable Cities.
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